Apparatus for delivering a glass stream

ABSTRACT

A method and apparatus for delivering a glass stream comprising a first inner layer and a second outer layer, comprising a generally vertical orifice, and delivering glass from a second source such that the glass from said second source provides an outer layer about the glass from the first source as it flows through said orifice. A resistance heated tube assembly is made of platinum or material having similar resistance heating properties and extends from a glass source to an orifice through which the glass flows from a glass source for the inner layer. The tube assembly includes a tube portion having an inlet end that communicates with the source for the outer layer and an outlet end that communicates with the source. The tube portion has an axis positioned at any angle ranging between the horizontal and vertical but preferably has an axis which is more vertical than horizontal. Flanges are secured to the ends of said tube portion, and the flanges are connected to an electric power supply. The cross sectional thickness of said flanges is preferably greater than the thickness of the tube portion. Each flange includes an annular groove adjacent its respective end of the tube portion into which the end of said tube portion extends. The flanges are welded to the tube portion. Flange heater modules surround each end of the tube portion.

This application is a division of application Ser. No. 09/030,402 filedFeb. 25, 1998 now U.S. Pat. No. 5,925,161, which is a division ofapplication Ser. No. 08/787,061 filed Jan. 22, 1997 now U.S. Pat. No.5,776,221, which is a continuation of application Ser. No. 08/374,371filed Jan. 18, 1995 and now abandoned.

This invention relates to a method and apparatus for delivering a glassstream for forming charges of glass.

BACKGROUND AND SUMMARY OF THE INVENTION

The purpose of this invention is to deliver a stream of molten glass, atmaintained temperature, to a remote location and particularly to combinetwo streams of molten glass in a location of limited size andaccessibility.

Existing glass coating techniques involve the introduction of multipleglass streams in the forehearth or furnace section of the glass formingoperation. This requires new equipment to be installed for the handlingof main glass stream as well as the coating glasses.

Typical patents showing such construction, for example, are U.S. Pat.Nos. 1,828,217, 3,291,584, 3,554,726, 3,960,530, 4,023,953, 4,217,123,4,299,609, 4,381,932 and 5,204,120.

Conventional forehearths for glass delivery are constructed ofrefractory brick. The glass is contained in a horizontal bath. Heat ismaintained by radiant heating from combustion burners above the bath.Bath depth is limited to about 10" due to the practical limitations ofinfrared heat penetration. Alternately, electric current may be passedthrough the molten glass to maintain temperatures.

In either case, the glass is contained within the refractory ceramicbrick. In a typical forehearth, the innermost refractories are verydense to resist glass attack. The outer layers are progressively lessdense for their insulation properties. The overall wall thickness istypically from 10 to 18 inches. The overall width of the forehearth isseveral feet, therefore the placement of two forehearths in order tocombine two glass streams is not possible.

The present invention provides for conveying glass from a remotelocation without the need for heavy refractories and radiant heating andin close proximity (4" to 12") to another glass stream.

The present invention is directed to a method and apparatus fordelivering a glass stream comprising a first inner layer and a secondouter layer, comprising a generally vertical orifice, delivering moltenglass from a first source through said orifice, and delivering glassfrom a second source such that the glass from said second sourceprovides an outer layer about the glass from the first source as itflows through said orifice.

Among the objectives of the present invention are to provide an improvedmethod and apparatus for conveying the glass from the second source toprovide the outer layer; wherein the glass is conveyed while efficientlymaintaining uniformity of temperature of the glass; wherein a tube isheated by resistance heating; wherein the tube is constructed andarranged for efficient and uniform temperature distribution along thelength of the tube; which is similar in function and smaller in designthan a conventional forehearth; which minimizes changes in existingglass delivery equipment for the primary glass stream; which allowscomplete glass containment; and which provides for desired hydrostatichead pressure of the secondary glass stream.

In accordance with the invention, a resistance heated tube assembly ismade of platinum or material having similar resistance heatingproperties and extends from a glass source for the outer layer to theorifice through which the glass flows from a glass source for the innerlayer. The tube assembly includes a tube portion having an inlet endthat communicates with the source for the outer layer and an outlet end.The tube portion has an axis positioned at any angle ranging between thehorizontal and vertical but preferably has an axis which is morevertical than horizontal. Flanges are secured to the ends of said tubeportion and the flanges are connected to an electric power supply. Thecross sectional thickness of said flanges is preferably greater than thethickness of the tube portion. Each flange includes an annular grooveadjacent its respective end of the tube portion into which the end ofsaid tube portion extends. The flanges are welded to the tube portion.Flange heater modules surround each end of the tube portion.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary part sectional diagrammatic elevational view ofa glass delivery system embodying the invention.

FIG. 2 is a part sectional elevational view of a resistance heated tubeassembly embodying the invention.

FIG. 3 is a sectional view of the tube assembly taken along the line3--3 in FIG. 2.

FIG. 4 is a part sectional view taken along the line 4--4 in FIG. 2.

FIG. 5 is a fragmentary elevational view taken along the line 5--5 inFIG. 1.

FIG. 6 is a fragmentary sectional view of the upper flange of thedelivery tube taken along the line 6--6 in FIG. 7.

FIG. 6A is a fragmentary sectional view of a portion of the deliverytube shown in FIG. 6.

FIG. 7 is a top plan view of the upper flange of the delivery tube.

FIG. 8 is a part sectional side elevational view of the upper flange.

FIG. 9 is a bottom plan view of the lower flange of the delivery tube.

FIG. 10 is a part sectional side elevational view of a lower portion ofthe delivery tube taken along the lines 10--10 in FIG. 9.

FIG. 11 is a schematic of the electrical heating system of the deliverytube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the invention relates to a method and apparatus fordelivering a glass stream comprising a first inner layer and a secondouter layer, comprising a generally vertical orifice 20, deliveringmolten glass from a first source 22 through said orifice 20, anddelivering glass from a second source 24 such that the glass from saidsecond source 24 provides an outer layer about the glass from the firstsource 22 as it flows through said orifice 20. Glass sources 22, 24comprise conventional forehearths.

In accordance with the invention, an electrical resistance heateddelivery tube assembly 30 is provided for delivery of glass from thesecond source 24 through a refractory orifice ring assembly 32 whichcontains glass from the source 22 and the source 24 to provide a moltenglass with a core of glass from source 22 and an outer layer from source24.

As shown in FIG. 2, the tube assembly 30 includes a tube 34 throughwhich the glass flows from a glass source for the outer layer. The tube34 has an inlet end that communicates with the source for the outerlayer and an outlet end. The tube 34 has an axis positioned at any angleranging between the horizontal and vertical but preferably has an axiswhich is more vertical than horizontal. Flanges 36, 38 are secured tothe ends of said tube 34. The tube 34 and flanges 36, 38 are made of amaterial that is corrosion resistant and can be electrically resistanceheated. Platinum and its alloys are the preferred material. Othermaterials can be used such as Inconel or molybdenum, but these lackglass corrosion and air oxidation resistance offered by platinum attemperatures normally encountered with molten glass applications.

Flanges 36, 38 are welded to tube 34 such that the weld is uniform andelectrically continuous around the joint, FIG. 6A. Thin spots causelocalized over-heating while thick spots cause localized under-heating.The cross sectional thickness of said flanges is preferably greater thanthe thickness of the tube 34 and, the flanges 36, 38 and tube 34 arepreferably uniformly thick. Referring to FIGS. 6-10 each flange 36, 38includes an annular groove 42 adjacent its respective end of the tube 34into which the end of said tube 34 extends and is welded. An electricalpower supply 50 is connected across the flanges 36, 38 by electricalsupply bars 52, 54 and connectors 56, 58 (FIG. 1).

Refractory blocks 60, 62, 64, 66, 68, 69 and 70 are placed about thetube 34 to provide mechanical support because the tube easily deforms atoperating temperatures. Insulation 72 is placed around the blocks 60-70to limit the loss of heat.

Referring to FIG. 11, in a typical example, a stepdown transformer(primary side) supplies (secondary side) power to the tube 30. The tubepower supplies just enough heat to overcome normal heat loss when glassis flowing through the tube and additional heat to moderate glass flowduring starting.

Additionally, flange heater blocks 60 and 70 provide auxiliary heat tothe flanged ends of the tube 34. Power for the flange heaters issupplied by an ordinary silicon controlled recitifier (SCR) durablepower controller. Temperature control is by means of a thermocouple-PIDcontroller.

The flange heaters are turned on only during start-up and shut-down. Theamperage necessary for each heater is different because they aredifferent sizes. Typically, they used only 5-25 Amps at 50-150 volts.

As shown in FIG. 5, there is a variable gap between refractory blocks 68and 69 to allow for longitudinally thermal expansion differences betweenthe refractory blocks 60-70 and the tube 34 while at operatingtemperatures. As shown in FIG. 5, the two sets of arrows on the wedgeshaped blocks indicate the position of steel support brackets. Thesebrackets support the entire weight of the refractory blocks. Since, theupper flange 36 rests on the upper flange block 60, the brackets mustalso support the weight of the tube 34 as well. The two arrows at thelower portion of the tube assembly indicate another set of steel supportbrackets. These brackets support only the pair of lower flange heaterblock 70 and refractory block 69.

The lower bracket is movable along the axis of the tube. When the tubeis hot, it expands downward, for example, nearly 1/2", which means theend of the tube extends 1/2" past the lower flange heater. Platinum isvery soft, at operating temperatures that can reach 2300 F. The exposedtube end and flange are subject to bending if not supported. Byadjusting the lower bracket downward, the lower flange heater block canbe brought into supportive contact with the flange 38.

In operation, it is desired that the tube be heated evenly, but not theflanges. This means that the flanges must be a better conductor than thetube. One way to achieve this is to make the overall cross-sectionalthickness of the flanges much greater than the tube. Another way is tomake flanges from a material with a much higher conductivity than thetube. Since the tube must carry a high current at high temperatures andprovide corrosion resistance to molten glass, it would be difficult tofabricate a tube/flange structure using dissimilar metals.

In practice, any type of glass can be used which in its molten statedoes not exceed the temperature limit of the alloy of tube 34.

Heating

The delivery tube assembly 30 conveys molten glass from source 24 toorifice 20. To be effective, the tube assembly 30 must supply heat tothe glass to make up for natural conduction losses, but it also mustmaintain a uniform temperature over its length to prevent thermalgradients in the glass.

The delivery tube assembly has two types of heating:

(1) Direct resistance heat from power being applied to each end, withthe tube acting as the resistor;

(2) External auxiliary heat applied to each end.

Tube Flanges

Wide flanges 36, 38 terminate each end of the tube 34. They allowsealing of the tube 34 to adjacent equipment, which in the exampleshown, is the underside of the spout feeding glass from the source 24above, and the upper side of the orifice ring assembly 32 into which theglass delivered. The flanges 36, 38 also serve as electrical connectionpoints.

Flange Design

The end flanges 36, 38 are designed to distribute electrical power (forresistance heating) into the tube portion 34. This design allowselectrical power to flow evenly around the periphery of the flangethereby heating the circumference.

The cross-sectional thickness of the flanges 36, 38 preferably is muchgreater than the tube 34, such that most of the resistance heatingoccurs in the tube 34 rather than the flanges 36, 38. Due to the natureof thermal conduction, heat loss will be greater at the ends of the tube34, so some degree of heating is needed in the flanges 36, 38. Referringto FIG. 6 to make up for thermal losses, the inner area of the flanges36, 38 where they join the tube 34, have a reduced cross-section 42,causing some resistance heating to occur in the flanges 36, 38.

Flange Sealing

For a good operation, the flanges 36, 38 must be hot in the inner edge,to minimize thermal disturbance to the glass flowing inside, and cooleron the outer edge to form a seal. The shape of the flanges 36, 38 andthe variations in cross-sectional thickness 42 are designed to meetthese conditions.

When molten glass flows through the tube 34, it flows into the hotflange sealing area and may even leak. However, by design, the outeredge of the sealing surface is at temperature below the devitrificationpoint of glass, typically about 1800° F. In this cooler area, the flowslows and stops as devitrification crystals form.

Flange Heating

For electrical resistance heating, power is applied to the flanges bylarge, water cooled copper clamps. The clamp area must be kept cool(under 200 F.) so electrical current transfer is maximized and copperoxidation is minimized.

Since cooling will draw heat from the flanges 36, 36 (over and abovenatural conduction losses), and, therefore the ends of the deliverytube, temperatures will be lower than along the length of the tube 34.The reduced cross section 42 in the flange causes an increase inresistance heating, thereby reducing this temperature loss.

Flange Seal Separation

Since the flanges 36, 38 are designed to form a seal with molten glass,they do not allow for easy separation. For this purpose, auxiliaryflange heating blocks 60, 70 serve to provide extra heat to remelt thesealed ends (from devitrified glass) so the tube can be separated frommating surfaces.

Satisfactory results have been obtained utilizing the apparatus shownand described where the tube assembly has its axis at an angle of about20° to the vertical and has a diameter of about three inches.

It can thus be seen that there has been provided a method and apparatusfor conveying the glass from the second source to provide the outerlayer; wherein the glass is conveyed while efficiently maintaininguniformity of temperature of the glass; wherein a tube is heated byresistance heating; wherein the tube is constructed and arranged forefficient and uniform temperature distribution along the length of thetube; which is similar in function and smaller in design than aconventional forehearth; which minimizes changes in existing glassdelivery equipment for the primary glass stream; which allows completeglass containment; and which provides for desired hydrostatic headpressure of the secondary glass stream.

What is claimed is:
 1. A resistance heated tube assembly for deliveringmolten glass comprising:a tube of corrosion-resistant electricallyconductive construction, and flanges secured to opposed ends of saidtube for connection to an electrical power source, said flanges havingflat portions with openings encircling said ends of said tube, inabutment with said ends of said tube, and being directly secured toopposed ends of said tube, an annular groove in said flat portion ofeach said flange surrounding said opening and said end of said tube,said grooves in said flanges being opposed to each other and formingportions of said flanges of reduced thickness directly secured to saidtube ends, so that said portions of said flanges secured to said tubeends are hotter than portions of said flanges spaced radially outwardlyfrom said tube ends.
 2. The resistance heated tube assembly set forth inclaim 1 including auxiliary heaters surrounding at least a portion ofsaid tube.
 3. The resistance heated tube assembly set forth in claim 2wherein said heaters are adjacent the opposed ends of said tube.
 4. Theassembly set forth in claim 1 wherein each said flange has a greatercross sectional thickness than the thickness of said tube, such thatsaid flanges are more electrically conductive than said tube.
 5. Theassembly set forth in claim 1 further comprising a plurality ofrefractory blocks about said tube between said flanges.
 6. The assemblyset forth in claim 5 wherein one of said flanges is disposed forabutment with an adjacent one of said refractory blocks.
 7. The assemblyset forth in claim 6 further comprises bracket means for supporting aone said refractory blocks opposite said one block.
 8. The assembly setforth in claim 7 further comprising means for accommodating thermalexpansion of said blocks between said one flange and said bracket means.